It is difficult to know why your girlfriend has changed because I have so few details about the relationship. Her behavior is unusual given the fact that you were recently engaged. It might indicate that she has met someone else. In your letter, there is no direct evidence of this but her behavior is not what you would expect at this stage of the relationship. Normally, an engagement would bring two people closer together. Her desire for interaction should have stayed the same or increased, not decreased.
It is important to communicate your concerns to her. You need and deserve a deeper explanation but it requires that you share your feelings and be honest about your concerns. Inform her that you are having difficulty understanding her change in behavior and that you need a more detailed explanation. Tell her that you are feeling unloved. The reasons behind the changes may not be as bad as you might think. Try not to jump to conclusions.
If you and she have difficulty communicating, then see a couples therapist before you are married. Many couples undergo premarital counseling. It is a very wise idea and I would highly recommend it in this situation. You need to be certain that getting married is the right choice. In addition, it is important that couples correct all problems in the relationship before they get married. Marriage will not automatically fix the problems in a relationship. The same problems that exist before marriage will exist after marriage.
If you have additional questions or would like to provide more information that may help me to better understand the relationship, please do not hesitate to write again. Check the “find help” tab at the top of this page to help you locate a couples therapist. I wish you and your girlfriend the best of luck. Please take care.